Preparation of secondary amines



ited States PREPARATION OF SECONDARY AMENES No Drawing. ApplicationFebruary 24, 1953, Serial No. 338,599

9 Claims. (Cl. 260-583) This invention relates to the preparation ofsecondary amines, and more particularly to the preparation of long chaindialiphatic secondary amines, such as dialkyl and dialkylene amines. Themethod of this invention can also be advantageously employed for thepreparation of aromatic secondary amines such as dibenzylamine, oraromatic aliphatic secondary amines, such as alkylbenzylamines.

The catalytic hydrogenation of long chain aliphatic nitriles to theprimary amines has been an industrial process for some time, but thedirect production of secondary amines from aliphatic nitriles has notheretofore proven commercially feasible in spite of the demand for longchain aliphatic secondary amines as synthetic intermediates in theproduction of quaternary ammonium compounds. Aiso, the preparation oflong chain aliphatic secondary amines from primary amines has not been aparticularly desirable commercial process.

In the preparation of long chain aliphatic secondary amines, either fromthe corresponding aliphatic nitriles or primary amines, it has beendifficult to obtain a high yield of the desired secondary amine product,and to have the product of good color and quality. Moreover, thereactions involved have been difficult to control, and the time requiredto compelte the reactions has been both variable and excessive. n theone hand, low temperatures with a correspondingly slower rate ofreaction has been found desirable to minimize decomposition and sidereactions, while on the other hand there has been a need for reducingthe time required to carry out the reaction. In other Words, one of theproblems involved is that of minimizing the reaction time whileobtaining high yields of a good quality secondary amine product.Heretofore, the reaction conditions have not been sufficientlyunderstood to permit "these results to be achieved.

It is therefore a general object of this invention to-provide animproved process for the production of secondary amines fromaliphaticnitriles, which-can also be used to produce secondary aminesfrom primary amines. Also, a more specific object of this invention isto provide a process of the character described which permits long chaindialiphatic secondary amines to be produced in high yields with agreatly decreased reaction time, While obtaining a product of good colorand quality. Another object is to provide a process which permitsreproducea'ole results to be obtained by the control of the importantreaction variables so that the desired results can be consistentlyobtained in commercial-scale production. It is a "still further objectof this invention to discover which factors or conditions are importantin achieving high yields of a good quality secondary amine product, andto determine what the critical ranges are for each of the factors andconditions. Further objects and advantages will appear as thespecification proceeds.

In practicing the method of this invention, aliphatic nitrilescontaining from -8 to .22 carbon atoms can be employed as the startingmaterial. Because of their availability, aliphatic nitriles containingfrom 1 2 to 13 carbon ice atoms are preferred. For example, the'alkyland alkylene nitriles derived fro'm'the fatty acids in common fatsand oils are admirably suited for further processing in accordance withthis invention. It is not necessary to separate the various chainlengths contained in naturalmixtures of such nitriles. In fact, nitrilesderived from mixtures of tallow fatty acids (tallow nitril s) andnitriles derived from mixtures of coconut oil fatty acids (coconitriles) are the preferred industrial materials. If desired, theprocess can-also be carried out with primary aliphatic amines containingfrom'8 to 22 carbon atoms, and preferably from 12 to 18 carbon atoms.Also, mixtures of such amines and nitriles of the character describedcan be employed.

In general, the process of this invention involves the catalytichydrogenation of aliphatic nitriles. Any hydrogenation catalyst can beemployed, although nickel catalyst, such as fresh Raney nickel arepreferred. The proportion of nickel catalyst to the nitrile or aminehasbeen found to be critical for obtaining both high conversion and highyields. In general, and particularly with Raney nickel, the amount ofcatalyst employed should range from about .4 to 3% by weight based onthe weight of nickel in the catalyst compared to the Weight of thenitrile or amine. With Raney nickel, best results are achieved when theproportion of catalyst to reactant is within the range from about .6 to2% by weight basedon the nickel in the catalyst.

The yield of secondary amine has been' found to be sharply increased byrigidly maintaining anhydrous conditions during the reaction. Sincewater would ordinarily be present in the reaction mixture, specialprecau tions must be taken. For example, ordinaryiRaney nickel containsabout 50% water, and both the nitrile and amine reactants will usuallycontain some moisture. Therefore, it is important to charge both thereactant and catalyst to the reaction vessel in a substantiallyanhydrous condition or alternatively, to dry the reaction mixture priorto the reaction. The drying of the reaction mixture can be carried outby heating the reaction mixture to a temperature above C. at atmosphericpressure, while bubbling a gas through the mixture. The temperatureshould be such as to vaporize the water, and suflicientgas should beadmitted to completely sweep the vaporized water out of the reactionmixture. In practice, drying temperatures of from to C. have been foundto be satisfactory, and either nitrogen or hydrogen can be used to sweepout the vaporized water with good results. it has also been founddesirable to agitate the reaction mixture during the drying step. Itwill be understood, of course, that the reaction should be conductedthroughout in such a way as to maintain anhydrous conditions. Even aslittle as 2% water has been found to be quite detrimental; therefore,the amount of water should be reduced below 1% by weight of the reactionmixture and preferably below .3% by weight. conditions should be asnearly anhydrous as possible.

The reaction can be carried out at temperatures ranging from to 210 C,although greatly improved results are obtained Within thespecifictemperature range of from to 198 C. If desired, the reaction can becarried out in two-stages, with the initial stage at temperature of from130 to 160 C., and the final stage at the temperatures just specified.However, excellent results have been obtained by carrying out bothstages of the reaction within the range from 180 to 198 C.

In one embodiment of this invention, the reaction is carried out in twostages with the reaction mixture being heated in the first stage at atemperature of from 130 to 210 C., and in the second stage at atemperature of from 170 to 210 C. However, the more specific temperatureranges set out above are preferred. in the first stage of in otherwords, the

6 the reaction, it is preferred to hold the ammonia formed in thereaction within the reaction zone while maintaining the reaction zoneunder an elevated pressure. In the second stage of the reaction, it ispreferred to remove the ammonia formed in the reaction from the reactionzone and to maintain a substantially atmospheric pressure in thereaction zone. More specifically, in the first stage of the reactionpressures of from l to 500 p. s. i. g. are satisfactory, while in thesecond stage of the reaction a pressure below p. s. i. g. is desirable.In practicing the invention in accordance with this two-stage process,the reactant and catalyst are charged to a pressure reaction vessel, andif water is present, they are subjected to a preliminary drying step asdescribed above. Thereafter hydrogen is introduced without ventingammonia and an elevated pressure is maintained during the first stage ofthe reaction. Samples of the reaction mixture are Withdrawn periodicallyand analyzed for the total amine content, that is, the combined percentby weight of primary and secondary amines. When the total amine contenthas reached a substantially constant value, the pressure is reduced andammonia is continuously removed from the reaction zone. The reaction canalso be carried out by employing alternate cycles of venting andhydrogenation after the amine content has reached a constant value.

It has been discovered that the presence of hydroxides in the reactionmixture is undesirable and tends to decrease the yield. The presence ofmetallic soaps is also undesirable for this reason. Therefore, thereaction mixture should be maintained substantially free of hydroxidesand metallic soaps. Since the nitrile and amine reactants will usuallycontain a small percentage of free fatty acids, the introduction of analkali or alkaline earth metal hydroxide is doubly undesirable, becausenot only does it introduce a hydroxide but also forms soaps by thereaction of the hydroxide with the free fatty acids.

It has also been discovered that the color of the secondary amineproduct can be greatly improved by bleaching it in situ during thecourse of the reaction. Furthermore, this bleaching cannot beaccomplished after the reaction has been completed. Therefore, it ispreferred to incorporate a small amount of an inert bleaching adsorbentin the reaction mixture, such as activated carbon or an adsorbent clay.In practice, from 1 to 3% of such adsorbent has been found to besatisfactory.

This invention is further illustrated by the following specificexamples.

Example 1 11,000 pounds of coconitrile was charged to an agitatedhydrogenation converter along with 150 pounds of Raney nickel catalyst(50% nickel). The reaction was heated in a slow stream of hydrogen to130 C. and held there for one hour to drive oil moisture. The hydrogenpressure was then raised to l75185 pounds and the temperature was notallowed to exceed 136 C. until the total amine had reached 80%. Afterthis time the temperature was allowed to go around 178 C. Alternatecycles of venting and hydrogenation were made until the end of thereaction. The reaction was terminated at the end of fourteen hours witha product that analyzed as 93% secondary amine and 4.8% primary amine.

Example II 11,000 pounds of tallow nitrile and 150 pounds of Raneynickel catalyst (50% nickel) were charged to a hydrogenation autoclaveequipped with an agitator. The reaction was then heated to 130 C.accompanied by agitation and a slow stream of hydrogen to help indriving off moisture. At the end of one hour the hydrogen pressure wasraised to 200 and the temperature held at 130 C. maximum until the totalamine had reached 90% (two hours). At this time the temperature wasallowed to rise to ISO-185 C. As in Example I, alternate cycles ofhydrogenation and venting were made throughout the run are 1,399

until the reaction was complete. The final product analyzed 91%secondary tuning and 2.6% primary amine.

Example 111 11,000 pounds of tallow nitrile and catalyst were charged tothe hydrogenator and dried as in Example II. At the end of the dryingperiod the reaction was heated to 195 C. as soon as possible instead ofholding it below 140 C. until the total amine reached -85% as inExamples I and II. The reaction was continued with alternate cycles ofhydrogenation and venting as previously. The final product had ananalysis of 90.6% secondary amine and 3.9% primary amine.

Example IV The hydrogenation unit was charged with 11,000 pounds oftallow nitrile and 150 pounds of 50% Raney nickel catalyst. The reactionwas conducted as in Example III. The product analyzed 92.2% secondaryamine and 3.9% primary amine.

Example V The hydrogenation unit was charged with 11,000 pounds ofcoconitrile and 150 pounds of Raney nickel catalyst (50% nickel). Thereaction was carried out as in Example HI. The product analyzed 92.2%secondary amine and 3.9% primary amine.

Example VI The hydrogenation unit was charged with 11,000 pounds ofcoconitrile and 150 pounds of Raney nickel catalyst (50% nickel). Thereaction was carried out as in Example III. The product analyzed 87.3%secondary amine and 3.4% primary amine.

In the preceding examples, the primary reactions occurring to producethe desired products can be represented by the following two equations,wherein R is a hydrocarbon chain:

While in the foregoing specification this invention has been describedby setting forth specific details of preferred embodiments thereof, itwill be apparent to those skilled in the art that many of the specificdetails and embodiments set forth can be varied considerably withoutdeparting from the broad idea of the invention.

I claim:

1. A process for the production of secondary ahphatic hydrocarbon amineswhich comprises preheating a mixture of a reactant selected from thegroup consisting of aliphatic hydrocarbon nitriles and amines havingfrom 8 to 22 carbon atoms and mixtures of said nitriles and amines, anda hydrogenation catalyst to remove substantially all of the watertherefrom; contacting said mixture under elevated pressure with hydrogenwhile maintaining within the hydrogenation zone the ammonia formed untilthe total amine content becomes substantially constant; venting theammonia formed from the hydrogenation zone; and thereafter continuingsaid hydrogenation reaction to substantial completion.

2. A process according to claim 1 wherein the reactants are coconitriles.

3. A process according to claim 1 wherein the reactants are tallownitriles.

4. A process for the production of secondary aliphatic hydrocarbonamines which comprises preheating to a temperature in the range of to C.a mixture of an aliphatic hydrocarbon nitrile containing from 8 to 22carbon atoms and a hydrogenation catalyst while bubbling a gastherethrough selected from the group consisting of inert gasesandhydrogen, to remove substantially all of the moisture from saidmixture; contacting said mixture at a pressure in the range of 100 to500 p. s. i. g. and a temperature in the range of 130 to 160 C. withhydrogen while maintaining within the hydrogenation zone the ammoniaformed until the total amine content becomes substantially constant;venting the ammonia formed from the hydrogenation zone; and thereaftercontinuing said hydrogenation reaction to substantial completion.

5. A process for the production of secondary aliphatic hydrocarbonamines which comprises preheating to a temperature in the range of 120to 150 C. a mixture of an aliphatic hydrocarbon nitrile containing from8 to 22 carbon atoms and a Raney nickel catalyst in an amount rangingfrom 0.4 to 3 weight percent based on the weight of nickel in saidcatalyst compared to the total Weight of nitrile, while bubblinghydrogen therethrough to remove substantially all of the moisture fromsaid mixture; further contacting said mixture at a pressure in the rangeof 100 to 500 p. s. i. g. and at a temperature of 130 to 160 C. withhydrogen while maintaining within the hydrogenation zone the ammoniaformed until the total amine content becomes substantially constantwithin the range of 75 to 90%; venting the ammonia formed from thehydrogenation zone; and thereafter continuing said hydrogenationreaction by alternate hydrogenation and venting until the reaction issubstantially complete.

6. A process for the production of secondary aliphatic hydrocarbonamines which comprises preheating a mixture of an aliphatic hydrocarbonnitrile containing from 8 to 22 carbon atoms and a Raney nickel catalystin an amount ranging from 0.4 to 3 weight percent based on the weight ofnickel in said catalyst compared to the total weight of nitrile, whilebubbling hydrogen therethrough to remove substantially all of themoisture therefrom; further contacting said mixture with hydrogen at apressure in the range of 175 to 190 p. s. i. g. and a temperature ofabout 135 C. while maintaining within the hydrogenation zone the ammoniaformed until the total amine content becomes substantially constant atabout to venting the ammonia formed from the hydrogenation zone; andthereafter continuing said hydrogenation reaction at a temperature inthe range of to 198 C., alternately hydrogenating and venting, untilsaid reaction is substantially complete.

7. A process according to claim 6 wherein there is incorporated into thereaction mixture an inert bleaching agent.

8. A process according to claim 7 wherein there is incorporated into thereaction mixture from 1 to 3 weight percent of finely divided activatedcharcoal.

9. A process according to claim 7 wherein there is incorporated into thereaction mixture from 1 to 3 weight percent of an adsorbent clay.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PRODUCTION OF SECONDARY ALIPHATIC HYDROCARBONAMINES WHICH COMPRISES PREHEATING A MIXTURE OF A REACTANT SELECTED FROMTHE GROUP CONSISTING OF ALIPHATIC HYDROCARBON NITRILES AND AMINES HAVINGFROM 8 TO 22 CARBON ATOMS AND MIXTURES OF SAID NITRILES AND AMINES, ANDA HYDROGENATION CATALYST TO REMOVE SUBSTANTIALLY ALL OF THE WATERTHEREFROM; CONTACTING SAID MIXTURE UNDER ELEVATED PRESSURE WITH HYDROGENWHILE MAINTAINING WITHIN THE HYDROGENATION ZONE THE AMMONIA FORMED UNTILTHE TOTAL AMINE CONTENT BECOMES SUBSTANTIALLY CONSTANT; VENTING THEAMMONIA FORMED FROM THE HYDROGENATION ZONE; AND THEREAFTER CONTINUINGSAID HYDROGENATION REACTION TO SUBSTANTIAL COMPLETION.